There have been a number of gravity operated shut-off valves designed and proposed. A ball valve is the commonly used tripping and flow blocking device. Since many designs rely their operations in positioning stability of the ball valve on a narrow pedestal or a grooved track, precise levelling of the valve installation is extremely critical. Therefore, either nuisance tripping or no-sensing condition of the valves are caused frequently by even minor levelling errors. Also some of the shut-off valves in the prior art hardly distinguish seismic shaking from the vibrations in the surrounding such as rattling from a passing car. This could cause occasional false tripping of the valve. In reviewing reset methods of the valves, mechanical resetting elements that penetrate the valve body often pose potential pressure leakage or malfunction in and around penetration points of the devices. Permanent magnets are often used to keep the sensing elements in ready position, with resetting means operable after the tripping. However, keeping the magnet as a resident member of the apparatus leaves room for vandalism and misuse.
It is the objective of this invention to significantly improve the reliability and integrity of the prior art, and resolve the problems of screening out non-seismic vibrations by introducing a free-rolling ball in a concave dish.
The most pertinent prior art is listed and reviewed, as follows:
U.S. Pat. No. 4,485,832 to Plemmons for an Automatic Gas Shut-Off Valve shows a ball valve on a circular channel and use of a reset rod.
U.S. Pat. No. 4,565,208 to Ritchie for a Seismic Shut-Off Valve shows multiple ball valves on a circular groove with a deflector. A reset rod is sued.
U.S. Pat. No. 3,747,616 to Floyd for an Earthquake Sensitive Shut-Off Valve shows a ball valve sitting in a saddle which is formed by inclined planes with a reset means that requires either opening of the valve or penetration through the valve body.
U.S. Pat. No. 4,715,394 to O'Donnell for a Gas Supply Safety Valve for Earthquake Protection shows a multi-axial grooved pedestal and a ball valve with a plunger type reset element.
U.S. Pat. No. 4,382,499 to Nelson for a Magnetically Resettable Emergency Shut-Off Valve shows a permanent magnet keeping a ball valve afloat and reset after tripping. This patent also intends to be more sensitive to vertical shock waves near an epicenter. The magnet is a resident element of the valve.
U.S. Pat. No. 4,785,842 to Johnson, Jr. for a Resettable Vibration-Actuated Emergency Shut-Off Mechanism shows a permanent magnet to keep the valve weight afloat and to adjust sensitivity.
Japan Patent No. 57-12,172 to Yagi for an Automatic Gas Shut-Off Device shows the use of a permanent magnet to keep the ball valve afloat and also to pickit up for a reset. The magnet stays as a permanent element of the valve.